The Biggest Extinction on Earth

Volcanic evidence

Beneath the frozen Siberian landscape, thousands of square miles of lava were discovered. Known as the Siberian traps, these testify to the biggest and most destructive volcanic eruption the Earth has ever experienced.

The scale of the flood basalt is difficult to grasp. Two hundred and fifty thousand cubic miles of lava were spewed out over almost a million years. According to UCL’s disaster scientist Bill McGuire, it would have been ‘hell on Earth’. “You would have had huge fractures slashing the crust open, and very fluid lava more than 1000 degrees [C or F?] in temperature, fountaining out and pouring off in all directions. Any life around there would be burnt,” he says.

Widespread consequences

But how did the Siberian traps affect life in the Karoo basin, on the other side of the world? The lava was certainly deadly, but scientists believe that the far-reaching effects of the Siberian traps lie in their ability to alter the Earth’s climate.

To understand the impact of this ancient flood basalt, it’s helpful to look at a more recent example: the Laki eruption of 1783. In this year, a 20-mile-long fissure spilled lava over 200 square miles of Iceland for a period of 8 months. Although no one actually died as a direct result of the lava flow, the flood basalt caused widespread destruction over the whole of Europe.

Along with red-hot lava, the Laki eruption spewed out 122 million tons of sulphur compounds. These combined with water vapour in the stratosphere to form tiny droplet clouds of sulphur dioxide. Acting like mirrors, the light-coloured droplets reflected sunlight back into space. Deprived of the sun’s heat and light, the entire northern hemisphere cooled. Temperatures dropped to 7ºC below the average in Iceland and in the western United States they dropped by 5ºC. The sulphur dioxide eventually fell to the Earth as acid rain which poisoned the struggling crops and eroded the soil. As a result, 50% of Iceland’s cattle perished and 20% of its population starved.

The Siberian traps were 250,000 times bigger than Laki. “The Laki eruption actually covered a relatively small area, about a third the size of greater London. If we look at the Siberian flood basalts they covered a huge area. The deposits cover an area almost the size of the whole central part of Russia, something like the size of the United States,” says McGuire.

Imagine the effects of Laki amplified two-and-a-half million times. The deadly belch of the Laki traps lasted for 8 months, but 250 million years ago, the massive slashes in the Earth’s crust let out their noxious gases for hundreds of thousands of years. The Siberian traps are the likely culprit for the extreme global climate change behind the mass extinction. A huge sulphuric sun-block brought darkness and savage cold. Many species perished from the sudden glaciation. Voracious acid rain gnawed vegetation for centuries on end.